溪頭柳杉碳吸存之評估

Abstract

全球暖化持續惡化，減少大氣二氧化碳含量為本世紀最主要之環境議題之一。陸域生態系中，森林經光合作用吸收及固定二氧化碳，有效減緩溫室效應。柳杉為台灣人工林主要樹種，因此，本研究應用光合作用速率評估溪頭地區柳杉的碳吸存效果，並探討光合作用與各項影響因子之關係。於台灣南投縣臺大實驗林溪頭營林區內，自2014年3月至2015年4月量測柳杉之光合作用速率與環境及生理因子，探討林木光合作用速率在不同方位及葉片形態下之差異、光合速率日變化與季節變化的主要影響因子、溪頭地區柳杉碳吸存潛力及葉表面積轉換公式之建立，以提供相關領域研究及森林經營參考。 由試驗樣木中發現：個體內葉片形態具有長短葉之差異，經葉綠素與可溶性蛋白含量之檢測發現長短葉平均含量相當，而個體間長短葉亦經光反應曲線測量，發現各光度下光合作用速率無顯著差異，初步研究顯示：長葉與短葉在個體內及個體間光合能力沒有顯著差異。在方位方面：分布於溪頭營林區空中走廊之柳杉，在東向與西向之光合速率日變化具有顯著差異，主要因東西向環境之光度及東西向柳杉蒸散速率之差異所致。柳杉平均一日之光合作用速率在濕季及乾季為分別為0.58及0.39 μmol m-2 s-1，顯示光合作用速率隨季節變化而變動。在濕季中光合作用日變化與季節變化最主要的影響因子為光度，蒸散速率次之，乾季亦以光度為最重要而相對溼度次之，雖兩季的影響因子相同但個別影響光合作用速率之程度不同；依據乾、濕季之光反應曲線顯示，乾、濕季之光反應曲線幾近重疊，顯示柳杉之光合作用潛力在季節轉換中無明顯變化。最後，進行各樣木之碳吸存評估，以累加方法與模式計算之每年碳吸存量分別為863.32及465.88 kg/ha，平均單株柳杉年碳吸存量為2.62及1.22 kg。利用線性校正模式，建立柳杉葉表面積(x)與雙面投影面積(y)之迴歸式，結果顯示：解釋率為72%，相關性為85%，在自由度為98中，95%信賴區間範圍為 [ 1.98 , 1.98 ]。

With the deterioration of global warming, decreasing the concentration of carbon dioxite becomes one of the main tasks on environment protection. In terrestrial ecosystems, forests absorb and fix CO2 via photosynthesis and reduce the global warming. Cryptomeria japonica is one of the primary plantation tree species in Taiwan. Therefore, the main purpose of this study was to measure the one-year carbon sequestration of the photosynthetic rate (An) in Cryptomeria japonica at Air Corridor in Xitou and studied the relationship of An and factors which influenced An . This study was conducted from March of 2014 to April of 2015, measuring An, together with the environmental and physioligical factors, in order to examine the effects of the An from two orientations and leaf morphology, clarify the main factor which effect An within diurnal and seasonal variations, determine the effect of one-year carbon sequestration in Xitou, and finally establish the transforming model from leaf projected area to leaf surface area. The leaf morphological difference was the length of leaf --- long leaf and short leaf between different leaves of C. japonica. After examining the content of chlorophyll and soluble protein, the experimental result showed that there were no difference between individual leaves. On the other hand, the light response curves are similar between long leaf and short leaf individuals. Therefore, the primary speculation was that the two types of leaves had similar photosynthetic capability. The An from east-orientation was different from that of the west, and that was the result of the difference in the radiation and leaf evapotranspiration rates between the two directions. Accounting for the An in wet (May to Semptember) and dry seasons, An was 0.58 and 0.39 μmol m-2 s-1 respectively. It showed that An could vary with seasons. Among all the environmental and physiological factors, radiation was most important factor which affected An within diurnal and seasonal variations, followed by the evapotranspiration rates in wet season and relative humidity in dry season. According to the light response curve, there was an overlap between dry and wet season, which showed the similar photosynthetic capability. Therefore, the characteristics of photosynthesis of C. japonica was no tramsmiting phenomenon within seasons. The amount of carbon sequestration per year was 863.32 kg/ha in accumulation method and 465.88 kg/ha in model method, and the average amount of carbon sequestration per tree was 2.62 and1.22 kg, respectively. Finally, when useing the linear calibration model to establish the transforming model for leaf projected area (y) to leaf surface area (x), the R2 is 72% and the correlation is 85%. Also, the 95% confidence interval for is [1.98 , 1.98 ] studied by the student’s t distribution with 98 degree of freedom.